Conventionally, so-called back-incident type photodetecting elements have been known. This type of photodetecting element is provided with a light-incident surface at the back surface side of a semiconductor substrate, and detects light made incident from the light-incident surface by a photodetecting section being at the front surface side. As a photodetecting device with such a photodetecting element, there is provided, for example, a semiconductor energy detector described in Patent Document 1. This semiconductor energy detector includes a BT-CCD (Back-Thinned CCD) for which a part of the semiconductor substrate is thinned on the opposite side to the photodetecting section and which is capable of detecting various types of energy beams including ultraviolet rays, soft X-rays, and electron beams at a high sensitivity, and used as, for example, a photodetecting section of a telescope for astronomical observation.    Patent Document 1: Japanese Published Unexamined Patent Application No. H06-196680